HEALDSBURG, Calif. — A series of deadly Northern California wildfires regained momentum Wednesday as winds whipped back up, pushing blazes through parched hills and vineyards and prompting additional evacuations from an arc of flames that has killed at least 17 people, destroyed more than 2,000 buildings and battered the region’s renowned wine-growing industry.

Local officials ordered a fresh round of mandatory evacuations in flame-battered Sonoma County, where at least 11 people have died and about 180 remain missing. One of the massive fires that has been ravaging the region since Sunday advanced overnight toward populated areas, prompting the additional evacuations, Sonoma County Deputy Sheriff Brandon Jones said.

The two biggest wine-country fires, known as Tubbs and Atlas, grew overnight as conditions worsened and had torched a combined 54,000 acres by Wednesday morning, according to Cal Fire.

The fast-moving flames have swept through densely populated neighborhoods in California’s wine country over the past two days, causing residents to flee from homes in the middle of the night as smoke filled their rooms.

One couple had to jump into their pool as flames rushed across their land, taking occasional gasps for air as flames lapped at their backs.

High winds that whipped up 17 large fires had faded earlier Tuesday and humidity increased, assisting an operation that has drawn resources from throughout the state and neighboring Nevada. But officials warned that the sharp northern wind, known as a Diablo, would return, allowing only a brief window for firefighters to carve clearings in place to stop the fires from spreading to vulnerable populated areas.

That wind returned Tuesday night, along with lower humidity levels.

The National Weather Service expects these “red-flag” conditions — including wind gusts up to 40 mph — to remain until Thursday in the North Bay Area, which includes Sonoma and Napa counties.

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More than 25,000 people have fled homes from seven counties north of San Francisco, filling dozens of shelters that state officials had hoped to consolidate in the coming days to provide more-efficient services. Many left houses with nothing, and officials acknowledged Tuesday that it could be weeks before some are able to return to what is left.

“These fires came down into neighborhoods before anyone knew there was a fire in many cases,” Cal Fire Chief Ken Pimlott said during an afternoon news conference. “This is just pure devastation and it’s going to take us a while to get out and comb through all of this.”

The scope of the damage prompted President Trump on Tuesday to approve federal emergency assistance to California, agreeing to a request made by Gov. Jerry Brown (D). The declaration, announced by Vice President Pence during a visit to the state’s Office of Emergency Services near Sacramento, provides immediate funds for debris clearing and supplies for evacuation centers, among other aid.

“I appreciate the fast response from the President,” Brown said in a brief statement.

The fires are the most destructive in what already has been a severe wildfire season for California and much of the West, where more than 8 million acres have been charred this year. In his letter to Trump, Brown said that nearly 7,500 fires have flared in California this year. Ten of them have prompted him to declare a state of emergency.

As a thick haze coated the sky and settled into the region’s canyons and valleys, state officials remained focused on rescue and containment.

The cause of the fires, which flared overnight Sunday and blew swiftly through more than 120,000 acres in the following days, was unknown and likely to remain so for some time.

Pimlott said the possibility that a lightning strike started the fires was “minimal.” In California, he said, 95 percent of wildfires are started by people, inadvertently or intentionally. “All of these fires remain under investigation,” he said.

State officials said that firefighters plan to use the advantageous weather to clear lines between the Atlas Fire and the city of Napa, and between the Tubbs Fire and the city of Santa Rosa — the largest in Sonoma County and gateway to the wine-tourism industry.

Those barriers would protect the areas from the south with the expectation that winds will shift back to the north in the days ahead.

Officials said the idea, in the case of the Tubbs Fire, was to prevent a “reburn” of Santa Rosa.

For Dylan Sayge, the original burn was devastating. He and his roommates were awake early Monday morning when they noticed an unusual sight outside their $1,600-a-month rental home in the Coffey Park neighborhood of Santa Rosa.

“We realized ash was falling from the sky,” said Sayge, 23, a musician who works at Trader Joe’s.

Soon after, online, they learned that a fast-moving fire had jumped Highway 101, propelled by howling winds. The power flickered and an explosion followed as a transformer blew nearby. They grabbed their three dogs — Cash, Willie and Shorty — and their cat, Apollo. Sayge packed up baby pictures and musical instruments.

They headed out in three cars and into a traffic jam. Sayge left behind a 1998 Ford Taurus that he had just been given as a gift. The dense smoke clouded visibility. He eventually made it to a friend’s home in Fairfax, down the road in Marin County.

The next day, he learned that the house was gone, the Taurus a charred husk.

“The world can change in any moment,” Sayge said. “Anytime.”

On Tuesday, the smoke, more than the weather, presented the biggest challenge to fire crews.

Warmer, high-altitude air pressed the smoke close to the ground, masking targets for the flight crews in some of the hardest-hit areas. Fire officials said that they used a record amount of flame retardant, pumped into the planes flying over the fire zones, in the initial hours of the fire.

The disruption to daily life in a region known as a calm, sometimes intoxicating, tourist destination was immense.

The 100,000 acres of vineyards — the focal point of California’s wine industry and the tourism business built around — remained threatened and, in some cases, damaged. The extent remained unclear.

Here in Healdsburg, a quaint town known to tourists for its wine tasting, food and antiques, the cast was dystopian.

Smoke as thick as fog shielded the sky. On the hillside, houses burned unattended with stretched-thin firefighters busy elsewhere. The wooden guardrails along Highway 101 — one of the state’s most prominent north-south arteries — smoldered after burning the night before.

More than a dozen schools were shuttered in the seven counties most affected by fires, and damage to the power grid meant that everything from charging cellphones to pumping fuel was curtailed.

Nearly 80 cell towers have been damaged or destroyed, complicating efforts by even those with a charged battery to contact relatives or call for emergency assistance. The National Guard plans to bring in communications equipment to bolster the network, which state emergency officials called a priority.

“People are anxious for information — glued to their phones, looking to get anything, news of their homes, friends, et cetera,” said Drew Halter, a county recreation supervisor helping run a shelter at the Petaluma Community Center, where 450 people had taken refuge. “They really arrived here with whatever they could carry with them.”

While people remained the focus of emergency crews, some private citizens organized on social media on behalf of animals imperiled by the fire line. A Facebook post asked: “Californians: If anyone has a horse trailer, Chalk Hill Ranch near Healdsburg needs emergency help. They have 54 horses in dire need of transportation off the ranch.”

Patrick King, 48, owner of the Soil King Garden Center in nearby Cloverdale, had taken in three evacuated horses by noon and expected a dozen more at least.

Fleeing the house, the Pompluns jumped into their pool as middle-of-the-night temperatures dropped into the 40s. They draped washcloths over the backs of their heads as they came up periodically to breathe, their backs exposed to the fire that was engulfing their home and land.

When the fire passed, they lay shivering on the hot stones of their patio, taking off items of clothes one at a time to let the heat from the stones dry them. Then, they walked out, and entered a neighbor’s abandoned home to borrow shoes and clothes. A Sonoma County deputy sheriff spotted them a mile and a half into their subsequent walk and drove them to an evacuation center located in a high school gymnasium.

Sitting at a metal folding table, the Pompluns discussed their next escape. On the table were two items they managed to preserve as they scrambled out of the house — their passports. They have a trip planned — and paid for — to Indonesia in a few days. They plan to be on the plane.

“We just have to get bus fare and figure out where to get to a bus stop,” Daniel Pomplun said.

Donosky reported from Windsor, Calif.; and Wilson and Phillips from Washington. Alissa Greenberg in Berkeley, Calif., and Kimberly Kindy, Joel Achenbach, Herman Wong and Amy B Wang in Washington contributed to this report.